Five adults, including a pregnant female, have been found murdered at a "horrific scene" at a home in southern Alabama.

A four-year-old child was found alive at the grisly murder scene in the city of Citronelle, about 30 miles north-west of Mobile.

Authorities are working to identify the bodies and notify relatives following the discovery on Saturday afternoon.

"Given the way the scene looks, we're going to be here a couple of days," said Captain Paul Burch of the Mobile County Sheriff's Office.

"It's obviously a horrific scene."

Mobile county district attorney Ashley Rich said the crime scene where five people were "brutally and viciously murdered" was the worst she had seen in 20 years as a prosecutor.

Suspect Derrick Dearman of Leakesville, Mississippi, was taken into custody after he walked into the Greene County Sheriff's Office on Saturday afternoon and confessed to the crimes, said Captain Burch.

He said he expects Dearman to face five or six counts of capital murder. One of the victims was a woman who was about five months pregnant.

Detectives are "attempting to establish the relationship between Dearman and the victims," said the sheriff's office on its official Twitter account.

It was clear that firearms and at least one other type of weapon had been used, said Captain Burch and Mr Rich.

However, Captain Burch added that it was not immediately clear whether the victims were attacked while sleeping or had put up a prolonged struggle.

Residents of the house called 911 to report a trespasser between midnight and 1am on Saturday, and Dearman appears to have been identified as the trespasser.

Captain Burch said he understood that Citronelle police responded to the call but did not find anyone.

The murders appear to have occurred later on Saturday morning.

A woman reported to Citronelle police on Saturday afternoon that she had been kidnapped and escaped.

Information from her account led Citronelle police to the house on Jim Platt Road.

Investigators believed the woman who contacted police had an undetermined relationship with Dearman.